This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2001-215688 filed in Japan on Jul. 16, 2001, the entirety of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a valve pause mechanism, and more particularly to a valve pause mechanism fitted between a valve lifter in reciprocating contact with a valve cam of a four-stroke internal combustion engine and a valve stem of a poppet valve.
2. Description of the Background Art
Japanese published unexamined patent application No. Hei 10-184327, the entirety of which is hereby incorporated by reference, describes an example of a valve pause mechanism of the background art.
As seen in FIGS. 14 to 16 of the present application, a valve lifter 03 fitted is into a cylinder head 01 of a four-stroke internal combustion engine so that the valve lifter 03 can slide in contact with a valve cam 02. The valve lifter 03 is also pressed by a lifter spring 04. A slide pin holder 05 is fitted into the valve lifter 03 and a slide pin 06 is inserted into the slide pin holder 05 so that the slide pin 06 can slide perpendicularly to a direction in which the valve lifter 03 is moved.
As shown in FIG. 15, the slide pin 06 is cylindrical. A stem working face 06a is formed by a part of the side of the slide pin 06 cut out flat. A stem through hole 06b is made perpendicularly to the central axis of the cylinder next to the stem working face 06a. The slide pin 06 pressed by a spring 07 is slid by oil pressure. A valve stem 08 is arranged so as to be pressed by a valve spring 09 so that the top end faces the stem working face 06a, or the stem through hole 06b respectively adjacent to the slide pin 06.
Therefore, where the slide pin 06 is located in a position in which the stem working face 06a faces the top end of the valve stem 08 (see FIG. 16), the valve stem 08 can be lowered via the slide pin 06. The valve can be opened or closed by lifting or lowering the valve stem 08 together with the valve lifter 03 lifted or lowered by the rotation of the valve cam 02.
When the slide pin 06 is moved and is located in a position in which the stem through hole 06b faces the top end of the valve stem 08 (a state shown in FIG. 14), the valve stem 08 is not untracked from the stem through hole 06b and cannot be lowered. Accordingly, the operation of the valve can be paused with the aforementioned arrangement.
The present inventors have determined that the inertial weight of a valve system increases by a quantity representative of the additional weight of the valve pause mechanism. A load of the valve spring is required to be increased corresponding to the increase in inertial weight and as a result, friction between the cam and the lifter increases.
As shown in FIG. 16, e.g., in the case of the slide pin 06 having the above-mentioned arrangement, the top end of the valve stem 08 is in contact with the stem working face 06a of the slide pin 06 in a valve operation state and a load is applied thereto. Stress is apt to concentrate on the deepest point P of an opening slightly within the stem through hole 06b at the back of the stem working face 06a. 
Therefore, the present inventors have also determined that durability of the slide pin against the bending stress in the valve operation state should be considered based upon the dimensional relation between the outside diameter of the slide pin and the stem through hole, and the relation of a load from the valve spring.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
An object of the present invention is to provide a valve pause mechanism provided with a durable slide pin of lightweight.
One or more of the objects of the present invention is accomplished by a valve pause mechanism for a four-stroke internal combustion engine comprising a valve cam; a poppet valve having a valve stem; a lifter spring; a valve lifter fitted between the valve cam and the valve stem, wherein the poppet valve is always pressed in a direction in which the valve lifter remains in an operating contact position with the valve cam by the lifter spring; a slide pin holder being fitted within the valve lifter; a slide pin being fitted into the slide pin holder, the slide pin being capable of sliding in a reciprocating motion in a direction perpendicular to the valve stem and having an upper surface and a lower surface; a stem working face on the lower surface of the slide pin; a stem through hole adjacent to the stem working face; a slide pin driving mechanism, the slide pin driving mechanism selectively applying the stem working face and the stem through hole to the valve stem by sliding the slide pin in the reciprocating motion; a chamfered portion being formed along the upper surface of the slide pin and extending along a portion of the stem through hole.
One or more of the objects of the present invention is also accomplished by a slide pin holder assembly for a valve pause mechanism of a four-stroke internal combustion engine comprising a valve lifter having a valve lifter spring; a slide pin holder being fitted within the valve lifter; a cylindrical slide pin being fitted into the slide pin holder, the slide pin being capable of sliding in a reciprocating motion in a direction perpendicular to the valve stem and having an upper surface and a lower surface; a stem working face on the lower surface of the slide pin; a stem through hole adjacent to the stem working face; a chamfered portion being formed along the upper surface of the slide pin and extending along a portion of the stem through hole.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.